Laser processing apparatus which perform processing such as fusion cutting by irradiating an object to be processed with laser light have conventionally been known. In general, this kind of laser processing apparatus includes a laser head provided with a condenser lens for converging laser light onto an object to be processed, whereas a light-transmitting hole is provided on the laser light entrance side of the laser head as an entrance pupil for allowing the laser light incident on the converging lens to have a fixed diameter (see, for example, Japanese Patent Application Laid-Open No. HEI 5-212571 and Japanese Utility Model Application Laid-Open No. HEI 3-18979).